The 3GPP defines a high-speed uplink communication which is referred to as “EUL (Enhanced Uplink)” or “HSUPA (High-Speed Uplink Packet Access)”.
In EUL, a mobile station UE is configured to send a data signal (MAC-e PDU) to a radio base station NodeB via E-DPDCH (E-DCH Dedicated Physical Data Channel).
Specifically, in EUL, the radio base station NodeB is configured to determine a mobile station UE to be scheduled for each time slot (TTI: Transmission Time Interval) and send a scheduling grant information (AG: Absolute Grant or RG: Relative Grant) to the scheduled mobile station.
Also, the mobile station scheduled in each TTI is configured to send MAC-e PDUs with TBS (Transport Block Size) according to the scheduling grant information (AG) received from the radio base station NodeB via the E-DPDCH.
Here, the mobile station scheduled in each TTI is configured to send MAC-e PDUs via the E-DPDCH with transmission power (or transmission amplitude) determined based on a “transmission power ratio (or transmission amplitude ratio) between the E-DPDCH and a general uplink communication control channel (DPCCH: Dedicated Physical Control Channel)” according to the AG.
In addition, in EUL of the “Time and Rate” system, only one mobile station UE is treated as a mobile station scheduled in each scheduling assignment period.
Also, in EUL of the “Time and Rate” system, the radio base station NodeB is configured to send a “Zero Grant (a first scheduling grant information)” to a mobile station UE currently scheduled at the time of switching between mobile stations UE to be scheduled, so that transmission of MAC-e PDUs via the E-DPDCH can be stopped.
However, in EUL of the “Time and Rate” system, even when a buffer of the currently scheduled mobile station becomes empty, the radio base station NodeB cannot switch the mobile stations to be scheduled until the radio base station NodeB receives “TEBS (Total E-DCH Buffer Status)” showing that the buffer is empty. Thus, there is a problem that a time period in which none of mobile stations UE sends MAC-e PDUs occurs to decrease utilization efficiency of the system.